More mathematical conundrums solved with mental arithmetic and poetry too | Lifestyle - Belfast Newsletter

The Reverend Isaiah Steen

Regular readers of Roamer’s page have by now become quite well acquainted with the Reverend Isaiah Steen, a Presbyterian minister, mathematician and author of a once-popular school text book called Steen’s Mental Arithmetic.

Frontispiece of the Reverend Steen's book

He published his widely-referenced book, followed by several additional print-runs, when he was a teacher in the Royal Belfast Academical Institution in 1842.

The book is a rich mine of information about all things mathematical, introducing formulas, equations, procedures and techniques for solving numerical problems “in the mind” the author explained “without the use of paper or slate, or anything else on which to perform the operation.”

Some of Rev Steen’s mathematical manipulations seem almost magical today, relying on brain-power rather than our ubiquitous, battery-powered calculators that effortlessly multiply, divide, add and subtract.

Work Out The Number of Shopping Days Till Christmas (2019!)

It’s probably this dependence on modern technology that baffled some folk when faced with the Rev Steen’s Table of Interest, a little mathematical chart that was shared on this page last week.

Based on Professor James Thomson’s calculations, another of Inst’s mathematics doyens, Rev Steen explained in his book that the Table of Interest “may be useful in finding the number of days from any day of one month to any day of any other month.”...

My apologies – I only included Rev Steen’s above-mentioned introduction to the chart last week and omitted his demonstration of how it works.

Rev Steen offered four examples to aid his readers, preceded by a general rule – “the table gives the days between any day of any month and the same day of any other month, which must be increased or diminished by the days in excess or defect.” 

In other words – if you want to know the number of days between today, December 12, and July 12, you just need to look at the December column of the chart and move horizontally across to where the vertical July column intersects. There you’ll find 212 – hey presto, the number of days between now and the 12th! 

I’ve checked it on my calculator and Rev Steen is absolutely right, but that’s from the same date this month to the same date in July.
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Source: Belfast Newsletter